JPH0376434A - Automatic equalizer - Google Patents

Abstract

PURPOSE:To always attain stable equalization of a signal even when a carrier of a transmission line is turned on/off or demodulation error frequently takes place due to a momentary change of a reception level by stopping updating of the equalization coefficient of an automatic equalizer when the level of a DC component is changed by a prescribed range or over. CONSTITUTION:When a DC component level of a reception signal outputted from a low pass filter 2 is fluctuated for a prescribed value, or over, that is, the carrier of a reception signal is interrupted, a deciding circuit 6 outputs a signal blocking the revision of equalization coefficient to a demodulation circuit 7. The demodulation circuit 7 makes an error signal fed back to an adaptive automatic equalization section 3 zero, thereby not revising the equalization coefficient of the adaptive automatic equalization section 3. Thus, an adverse effect such as remarkable deterioration in the equalization coefficient of the adaptive automatic equalization section 3 so as to disable the equalization of normal signal in the case of intermittent carrier of a reception signal is prevented, and an always stable signal is equalized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an automatic equalizer that is built into a demodulator and that updates equalization coefficients sequentially in accordance with error components of a signal.

(Prior art) Conventionally, demodulators such as high-speed modems that use voice bands have built-in automatic equalizers for correcting line distortion. Initially, this automatic equalizer had a means called training. After setting the equalization coefficients of the equalizer to the optimal state using the Adapter, the signal error component from the ideal point is then fed back to the automatic equalization unit, thereby enabling optimal automatic equalization to be performed at all times. Some act as type equalizers.

However, such an adaptive automatic equalizer has the following problems. That is, when the reception level changes, a demodulation error occurs in the demodulator until automatic gain control (AGC) operates. At this time, significant signal error components are fed back to the adaptive automatic equalizer, and the equalization coefficients of the adaptive automatic equalizer, which successively updates the equalization coefficients, deviate significantly, and subsequent automatic equalization This has the disadvantage of adversely affecting operation. In order to avoid this inconvenience, the amount of feedback is suppressed when the signal error component is fed back to the automatic equalizer.

In this case, the feedback coefficient to be suppressed is called a correction coefficient of the equalizer, and even if this correction coefficient is set to a small value and an error component occurs due to factors such as instantaneous level fluctuations, the equalization coefficient of the adaptive automatic equalizer It is possible to prevent a significant shift in the value and to suppress an adverse effect on subsequent equivalent operations.

However, even if such a method is used, if fluctuations in the reception level occur frequently, the deviation of the equalization coefficients of the adaptive automatic equalizer will increase, causing the inconvenience that the equalizer will diverge. .

In addition, when the carrier of the transmission path through which the signal is transmitted is interrupted or interrupted, an automatic equalizer that continuously performs adaptive equalization from the equalization coefficient previously set through training can determine this based on the interruption of the carrier. During this time, adaptive equalization is performed, and at this time, even the small received signal just before the carrier is cut off is adaptively equalized. At this time, the equalization coefficient shifts significantly, and the equalization operation does not resume normally. The drawback was that it was no longer carried out.

(Problems to be Solved by the Invention) As mentioned above, in the conventional adaptive automatic equalizer, training is continued from the previous equalization coefficient and adaptive equalization is performed, especially when the carrier of the transmission path is interrupted. This is because automatic equalization is performed even on the small received signal just before the carrier is cut off, and the signal error component generated at this time is fed back, making the equalization coefficient a value significantly different from the normal value. However, there was a drawback that the automatic equalization operation was adversely affected.

Therefore, the present invention aims to eliminate the above-mentioned drawbacks by always performing a stable signal equalization operation even when the carrier in the transmission path is interrupted or interrupted or when demodulation errors occur frequently due to instantaneous changes in the reception level. The purpose is to provide an automatic equalizer that can perform

[Structure of the invention]

(Means for Solving the Problems) The present invention equalizes a received signal whose level is kept constant by auto gain control based on an equalization coefficient, and also performs the above-mentioned adjustment in response to an error component of this equalized signal. In an automatic equalizer that updates an equalization coefficient, a filter means for extracting a DC component of a received signal outputted through the auto gain control, and a level of the DC component of the received signal extracted by the filter means is detected. level detecting means; determining means for determining whether a change in the level of the DC component detected by the level detecting means is greater than or equal to a predetermined range; and a control means that performs control to prevent updating of the equalization coefficient when it is determined that the equalization coefficient has changed.

(Operation) In the automatic equalizer of the present invention, the filter means extracts the DC component of the received signal output through the automatic gain control. The level detection means detects the level of the DC component of the received signal extracted by the filter means. The determining means determines whether a change in the level of the DC component detected by the level detecting means is greater than or equal to a predetermined range. The control means performs control to prevent updating of the equalization coefficient of the automatic equalizer when the determination means determines that the level of the DC component has changed by more than the predetermined range.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a block diagram showing an embodiment of an automatic equalizer of the present invention. 1 is a level of a received signal. 2 is a low-pass filter (LPF) that extracts the DC component from the signal output from the AGC circuit 1; 3 is a low-pass filter (LPF) that successively updates the equalization coefficient according to the signal error component fed back from the demodulation circuit 7; 4 is a setting circuit that sets a reference value for determining the fluctuation range of the received signal; 5 is a setting circuit that sets the DC component output from the LPF 2 and the setting circuit 4; A comparator 6 determines whether or not to update the correction coefficient of the adaptive automatic equalizer 3 based on the magnitude of the difference output from the comparator 5. A determination circuit 7 demodulates the signal equalized by the adaptive automatic equalization unit 3, and a demodulation circuit that feeds back the signal error component detected at this time to the adaptive automatic equalization unit 3; This is the transmission line through which the data is transmitted.

Next, the operation of this embodiment will be explained. The signal received via the transmission path 8 is outputted to the adaptive automatic equalizer 3 and the LPF 2 after its level is made constant by the AGC circuit #t1. The LPF 2 extracts a DC component from the input constant level signal and outputs it to the comparator 5. Here, the output of the LPF 2 is the DC component of the signal received via the AGC circuit 1, but if the received signal exists, the value of this DC component will be constant. Therefore, comparator 5 is LPF2
The DC component level output from the controller 4 is compared with a reference value preset in the setting circuit 4, and the difference is output to the determination circuit 6. A determination circuit 6 determines whether the value of the difference output from the comparator 5 is within a certain range (threshold value), and if it is within a certain range, a signal for updating the equalization coefficient is sent to In this case, a signal is output to the demodulation circuit 7 to prevent updating of the equalization coefficients.

On the other hand, the adaptive automatic equalization section 3 equalizes the received signal output from the AGC circuit 1 and outputs this equalized signal to the demodulation circuit 7. The demodulation circuit 7 demodulates the input equalized signal, determines an error signal at the time of demodulation, and feeds it back to the adaptive automatic equalizer 3. The adaptive automatic equalization unit 3 updates the equalization coefficients based on the error signal fed back from the demodulation circuit 7, and equalizes the input received signal based on the new equalization coefficients. However, when the demodulation circuit 7 receives a signal to prevent updating of the equalization coefficients from the determination circuit 6, the error signal to be fed back to the adaptive automatic equalization section 3 is O, and the equalization coefficients of the adaptive automatic equalization section 3 are set as O. Do not update.

According to this embodiment, when the DC component level of the received signal output from the low-pass filter 2 fluctuates by more than a predetermined value, that is, when the carrier of the received signal is discontinued, the demodulation circuit 7 outputs the error signal detected at this time. The equalization coefficients of the automatic equalizer 3 are not updated without being sent to the adaptive automatic equalizer 3. Therefore, it is possible to prevent negative effects such as when the carrier of the received signal is cut off or continues, the equalization coefficient of the adaptive automatic equalization unit 3 shifts significantly, making it impossible to perform normal signal equalization. Signal equalization can be performed.

Also, if the level of the received signal changes momentarily,
Since the DC component level of the received signal does not change due to the time constant of the low-pass filter 2, stable automatic equalization can be performed without unnecessary updating of the equalization coefficients of the adaptive automatic equalizer 3 at this time as well. I can do it.

〔Effect of the invention〕

As described above, according to the automatic equalizer of the present invention, a stable signal equalization operation is always possible even when the carrier in the transmission path is interrupted or interrupted, or when demodulation errors occur frequently due to instantaneous changes in the reception level. It can be carried out.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic equalizer of the present invention. 1...AGC circuit 2...Low pass filter 3...Adaptive automatic equalization section 5...Comparator 6...Determination circuit 7...Demodulation circuit

Claims (1)

[Claims] The automatic equalizer equalizes a received signal whose level is kept constant by automatic gain control based on an equalization coefficient, and updates the equalization coefficient in response to an error component of this equalized signal. filter means for extracting the DC component of the received signal outputted through auto gain control; level detection means for detecting the level of the DC component of the received signal extracted by the filter means; determining means for determining whether a change in the level of the DC component is greater than or equal to a predetermined range; An automatic equalizer comprising: control means for controlling updating of coefficients.